5. Accuracy of Wavelengths

Our estimate of the uncertainty of the photographically measured
wavelengths is based on several considerations:

The standard deviation of our polynomial fits for the
Cu II reference lines in the Pt/Cu lamp was
typically 0.0010 Å.

The standard deviation of our polynomial fits for the Pt lines used
as internal standards for measurements in the Pt/Ne lamp was
typically 0.0015 Å.

A comparison of a group of about 100 lines measured by different
operators on different plates and taken with different grating
rotations in the region 1470 Å to 1520 Å showed an
average deviation of 0.0001 Å and a rms difference of
0.0014 Å. In general, our separate measurements of the
wavelengths of individual lines agreed to about this level of accuracy.

A comparison of the wavelengths of 37 lines of
Pt II in the region 2247 Å to
3700 Å that were measured in this work and independently by
Engleman [7] shows an average deviation of
0.0003 Å and a rms difference of 0.0019 Å.

For the 508 lines of Pt II whose wavelengths
can be calculated from the optimized level values, the rms difference
between the calculated and observed wavelengths is about
0.0015 Å.

A comparison of our measured wavelengths for impurity lines appearing
in the Pt/Ne lamp with standard wavelengths for these lines shows an
average deviation of 0.0003 Å and an rms difference
of 0.0015 Å.

Based on these comparisons we estimate an uncertainty of
± 0.0020 Å for the wavelengths measured photographically.

As mentioned above, the wavelengths of classified lines of
Pt II in the atlas which have numbers in the CODE
column are those derived from the optimized level values. The uncertainties
of these wavelengths are taken to be the square root of the sum of the squares
of the uncertainties of the combining levels as given by Reader, Acquista,
Sansonetti, and Engleman [7]. They are listed in
the far right column under the heading CODE in units of 0.0001 Å.

The uncertainties of the photoelectrically measured lines were estimated
by comparing the measured wavelengths of Pt II lines
observed only in the photoelectric scans with calculated Ritz wavelengths for
the same lines. The standard deviation of the differences was about
0.006 Å for lines below 2030 Å and about
0.015 Å for lines at longer wavelengths. Based on these comparisons
we estimate the uncertainty to be ± 0.01 Å for lines below
2030 Å and ± 0.02 Å for lines above 2030 Å.

The uncertainties of lines whose wavelengths have been taken from the
literature are discussed in some detail in the notes to the atlas. Most of
these uncertainties are less than 0.001 Å and virtually all are
less than 0.002 Å.

The cathodes of the lamps used in this work and with GHRS contain isotopes
of Pt in their natural abundances. Some lines of Pt I
and Pt II show appreciable isotope and magnetic
hyperfine structure (hfs). At the resolution of our spectrograph (and also
GHRS) almost all Pt lines appear sharp and symmetric. A few lines show
evidence of unresolved structure and appear wide, hazy, or asymmetric on the
photographic plates. These lines are noted (W, H, L, or S) adjacent to their
intensities in the atlas. Lines showing partially resolved structure are noted
in the atlas as being complex (C). A few hyperfine patterns occurred in the
photographic data as three fully resolved features and were measured as
separate lines.

For GHRS and other instruments with resolving power of 105 or less,
the existence of hfs in some lines should present no problem in using the
present list of Pt lines for wavelength calibration. To achieve the highest
accuracy, lines with notations indicating detectable unresolved structure
should not be used. For instruments with resolving limits significantly below
0.02 Å, structure may be observed in many additional Pt lines, and
our present wavelength list may not be adequate for calibration purposes. Thus,
for calibration of spectrographs having much higher resolution, it may be
desirable to develop calibration wavelengths based on a lamp whose cathode
contains a single even isotope of Pt.